1. Field of the Invention
The invention relates to power regulation, and more particularly, to low dropout (LDO) regulators capable of preventing damage caused by a short circuit or a heavy load.
2. Description of the Related Art
A regulator converts an unstable power supply voltage into a stable power supply voltage. A low dropout (LDO) regulator has a low input-to-output voltage difference between an input terminal where an unstable power supply voltage is inputted and an output terminal where a stable power supply voltage is outputted. “Dropout voltage” refers to the input-to-output voltage difference, whereby the regulator ceases to regulate against further reductions in input voltage. Ideally, the dropout voltage should be as low as possible, to allow the input voltage to be relatively low, while still maintaining regulation. Thus, assuring that the input-to-output voltage difference is low and minimizing power dissipation and maximizing efficiency are important.
Generally, the conventional LDO regulator includes a protection circuit such as an over-current protection circuit so as to protect the circuit during abnormal operating conditions. For example, the over-current protection circuit maintains the output current (IOUT) of the LDO at a predetermined current value and controls the LDO to reduce the output current (IOUT) when an output voltage (VOUT) thereof is lower than a predetermined value caused by a heavy load (i.e. a short circuit occurs).
However, the foldback voltage of the conventional LDO is not accurate, the foldback voltage is affected by ambient temperature and adjustment range of the foldback voltage is limited. Further, after the output voltage is foldback, the output current correlates with the ambient temperature, other circuit parameters and process parameters, and thus, control of the output current is difficult.